In radial inward flow turbine nozzles, erosion of the inner surface of the nozzle by dirt particles thrown outward by the turbine wheel blades can greatly reduce the life of the nozzle. It is believed that any particles introduced into the nozzle ring continue to spin inside the ring at a high velocity for many revolutions until the particles are broken down to fractions fine enough to be drawn along with the turbine air and discharged through the eye of the impeller. Since a particle thus rotates many times inside the nozzle ring it produces continuous wear on the inner surface of the nozzle until it is reduced in size and discharged.
Attempts to alleviate this problem have included filtering the fluid before it enters the turbine nozzle. To do this, however, 5 to 10 percent of the air has to be discharged as filter purge air at an average of at least one PSI pressure drop of the full air stream. In addition, the filter, possible bypass, and the required controls attendant thereto add weight to the system. Thus this solution is not satisfactory for many applications.
Alternately, a composite nozzle including an inner nozzle ring of an erosion resistant material such as described in U.S. Pat. No. 3,737,247, can be utilized. While this has proven to be satisfactory in many applications, it still does not alleviate the basic problem.